Vibrator



Nov. 25, 1958 w. c. BuRGEss, JR., ET AL 2,851,548y

VIBRATOR Filed Feb. 20, 1957 3 Sheets-Sheet 5l 37 .sa a5 E 4311, 32 39 Il V W Q W Ik \/l\\\ WIV j 42 32 43 a4 sa sa 42 INVENToRs MDW/nnen C. Bunesss,JR.

WiLLAm H. SreRaeN'rz 5f M Nov. 25, 1958 w. c. BURGEss, JR., ETAL 2,851,548

VIBRATOR Filed Feb. 2o, 1957 s sheets-sheet s loo P5167 o o n 2 3 4 END CLEARNCE lNcHE's A1' 'CUT' oFF". f1 5.- 11

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lr- 12 END CLEARANCE, lNcHEs ATcuT oFF' INVENToRs 15' WARREN C. BuRaessJa. l

WlLuAM H. STEReEm-z United States Patent VIBRATR Warren C.l Burgess, Jr., North Olmstedgv'Ohio, and 'William H; Sterbentz, Malibu,- Calif.; said Sterbentz assignor to said Burgess ApplicaionFebruary'Zll, 1957; Serial Nar/641,326

w -11 Claims. p (Cl. 12117) This invention relates to vibratorsl o'f -the type commonly associated with screening operations, in special vibrating conveyor arrangements, in packing andpackaging operations, andA in many other industrial applications. More specifically, this vibrator is ofthe type employing a--reciprocatng piston driven' byl iluid pressure.

This application is a continuation-in-part of our copending application Serial No. 346,204, filed `April 1, 1953.

An object of our invention is to provide an improved vibration-inducing device which provides increased power for a given line pressure. A further object of our invention is the production of a vibrator having an increased frequency of vibration for a given line pressure.

A further object of this invention is the production of a non-impacting pneumatic vibrator and vmethod of inducing vibration.

Another object of our invention is to provide a vibrator of simple construction having an increased'efliciency and producing superior results over the vibrators which have been employed in the past.

Other objects and advantages of our invention will become apparent as the description proceeds.

To the accomplishment of therforegoing and related ends, said invention, then,` comprises the ffeatures hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting lforth in detail certainv illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways invwhich the principle of the invention may be employed.

Referring to the drawings:

Fig. 1 is a side view of one embodiment of our vibrator assembled and secured on a mounting base;

Fig. 2 is a bottom view of our device showing -a partial section of our vibrator;

Fig. 3 is a side cross-sectional view of our vibrator;

Fig. 4 is a sectional view taken alongthe line 4 4 of Fig. 2;

Fig. 5 is a sectional view 2;'and

Fig. 6 is a side cross-sectional view of an alternative form of our improved vibrator.

Figs. 7, 8 and 9 are side cross-sectional-views of the same device which is an alternative form of our improved vibrator showing various positions of the piston.

Fig. 10 is a side cross-sectional view'of another form of improved vibrator Aillustrating the term end clearance.

Fig. 1l is a graph plotting the frequency in cycles per minute against the end clearance.

Fig. l2 is a graph plotting a number proportional to the power against the end clearance.

Referring. more particularly to'Fig. 1, the vibrator casing 1, or cylinder, is a metallic casting having aicentral circular bore therethrough and is securelyfm'ounted on the mounting base 2 by means of bolts '3' and nuts 6. The casing 1 at the end which is secured to the mounting base taken along line 5 5 in Fig.

Y is provided with hole 7 which isdrilled through the vibra- Ce *Patented- Nowfzs, v195s p of the machining operation, is secured by inserting therein is directed alternately into recesses to the system.A Such inlet core plug 10 which provides an airtight seal. The oppositeend-of -the casing isA likewise secured airtight by means of an end bell 11 mounted over gasket vr29V and rmly held in position on the casing by bolts 12.

Mounted within the casing 1 is a cylindrical piston 14, the sides of which are in-sliding contact with the machined inside surface of the casing 1. The piston 14 is mounted so as to provide for its lreciprocating movement in an axial direction within the casing 1.

The casing 1 is further provided with an-inlet port indicated at 15 to permit the introduction' of fluid pressure into the system. This inlet port 15 vmay be provided with a conventional inlet one-way shut ol valve or any other conventional inlet valve to regulate the fluid ilow port 15 leads to a circularly grooved chamber'16 disposed between the piston 14 and the casing or cylinder 1 where the uid under pressure 17 and 18 inthe piston 14 which in turn carry the lluid under pressure through ducts 19 and 20 respectively to the end chambers 21 and 22 respectively of the casing 1. Thus, as the piston 14 is driven in a reciprocating manner, the fluid under pressurewill alternately be directed to end chambers 21 and 22 of the casing 1. Following the direction of the Huid into end chamber 21, such uid is then released to the atmosphere through exhaust ports 23. Similarly following the direction of the fluid into end chamber 22 such fluid is released to the atmosphere through exhaust ports 13.

Our vibrator may be further equipped at the terminus of ducts 19 and 20 with a fast-acting cut-off valve, one embodiment of which is morefully illustrated in Fig. 5.

As shown in Fig. 5, this cut-olf valve consists of a small piece 24 of high tensile strength spring steel secured to the piston 14 by means of screws 25 at yone end and the other end extending over and securely covering -the terminus of duct 19. To ensure an airtight seal of duct 19 by means of the piece 24 of spring-steel, a gasket 26 is mounted in a recess provided at the terminus of duct 19. In order to ensure Athat this fast-acting cut-olic valve is not damagedwhen the piston reciprocates within the casing, each end of the piston 14 is machined so as to provide a circularly raised ring 27 which acts as a bumper to prevent damage to the cut-olf valve should the piston strike the end of the casing 1 or end bell 11.

More particularly describing our-'vibrator and its mode of operation, a source of iluidunder pressure, such as compressed air, is required for its operation. Such air under pressure is introduced to the vibrator through the inlet port 15. As shown in Fig. 3, the piston 14 is located in the casing 1 approaching` end bell`11. -When the piston is so located, the air introduced under pressure through inlet port 15 passes into circular chamber 16 and into recess 17l which at that point in the cycle is in direct contact with circular chamber 16. The air underpressure then passes through duct 19 into end chamber 21 of the casing 1. Such air pressure drives the piston 14 in the direction of the sub-base v8 until such time as this relative movement of the piston to the 'left eliminatescontact between recess 17 and circular chamber-16 at which point circularchamber 16 establishes contact with recess v18 directingthe air under pressure through duct 20.into end chamber 22,4,thus driving,v the piston back towardv end bell`11 to complete the cycle.` Exhaust ports 13. and 23 are located in casing 1 so thatlonce the air has been i11- troduced into` either end chamber 21S or'22 andv such" air pressure `hasd`riven the: piston 1,4 in the desireddirec'tion,

chamber is permitted to discharge to the atmosphere 3 through exhaust ports 13 or 23. For example, with the piston in the position as shown in Fig. 3, the air in chamber 22 will be exhausted to the atmosphere through exhaust ports 13 and the air pressure in end chamber 21 will be equal to or greater than line pressure, thus effecting a force tending to drive the piston to the left.

The mode of operation of our vibrator as described above is that commonly employed in many vibrators presently available, and such vibrators employ principles commonly well known to those in the trade.

Notable examples of the prior art to which general reference has been made include the patent to Richwood, 835,290 and the patent to Cannon, 2,590,155. Although these devices are of the silent or semi-noiseless type, they can be distinguished from the silent or semi-noiseless type herein described in that it has now been found that the power output in these devices can be vastly improved by means of so constructing and arranging the parts that the pressure of the air in the end bell or end chamber is allowed to exceed the line pressure on the gas actuating7 the device. The terminal positions of the Richwood device indicate that the pressure in the end bell does not exceed line pressure, and in the Cannon device by means of a second entry port, Cannon insures that the pressure in the end chamber never exceeds line pressure. It has been found that by utilizing the piston itself as a fast-acting cut-off valve as herein described whereby all passages into and out of the end chamber are sealed during a portion of the stroke, the power output of the device can be greatly improved.

We have found that the inclusionof a fast acting cutoff valve in the fluid pressure system produces these vastly superior and unexpected results. The fast-acting cutoff valve may take the form of a flapper valve 24 as shown in Figs. 2 and 3, or, as previously indicated, the

piston itself may serve as its own fast-acting cut-off valve.

Our vibrator employing this fast-acting cut-oit valve will affect the mode of operation of the vibrator in the following fashion. While the piston 14 is being driven towards the sub-base S of the casing 1, the air remaining in the end chamber 22 escapes to the atmosphere through exhaust ports 13 until such time as the relative movement of the piston towards sub-base S causes the openings of exhaust ports 13 located near end chamber 22 to be sealed by the walls of the piston 14. At this point in the cycle "and as the piston continues to move towards sub-base 8,

the air remaining in end chamber 22 is trapped therein, and Without the addition of our fast-acting cut-off valve, the pressure build-up in end chamber 22 soon reaches and exceeds the line pressure which has become available through duct 20, recess 18 and circular chamber 16. At this point, the increased pressure in end chamber 22 feeds back into the line, dissipating this energy created by the momentum of piston 14, until the combination of the line pressure and the increased pressure of chamber 22 nally stops the movement of the piston towards subbase 8 and initiates relative movement of the piston towards end bell 11. The addition of our fast-acting cutoff valve permits the line pressure to freely flow into end chamber 22 when recess 18 and circular chamber 16 are in relative contact. However, as soon as the exhaust ports 13 are closed by the surface of the piston 14 in its movement towards sub-base 8, and when the pressure build-up in end chamber 22 approaches, equals or slightly exceeds that of the line pressure, our fast-acting cut-off valve functions responsive to the pressure differential to completely seal ott end chamber 22 so as not to permit the pressure feed-back into the line.A This fast-acting cnt-oft valve thus traps the remaining air in end chamber 22 and utilizes the energy created by the movement of the piston towardsrsub-base 8v by further compressing the air remaining, having the eifect of decelerating the piston towards sub-base 8 in a much more rapid manner and also increasing the acceleration of the piston towards end bell 11. v

Ament'of they piston 33 to the right.

Such a fast-acting cut-off valve is likewise mounted at the opposite end of the piston 14 at the terminus of duct 19 and functions in a similar manner to that above described.

While it is obvious that many different types of cut-oft valves may be employed in our invention, we have tested many different kinds of cut-off valves and have found that our superior results are achieved only if such cut-off valve is a fast-acting valve. The term fast-acting cut-oit valve as employed in this specification and the appended claims is intended to refer to a cut-off valve located in the uid pressure system intermediate the inlet port and the end chambers of said casing which is of the type capable of rapidly operating at a rate at least equal to the frequency of the pistons movement. Thus, the fast-acting cut-oit valve must in effect be capable of functioning in synchronism with the frequency of movement of the piston back and forth. This is necessary in order that the air trapped alternately in each end chamber be utilized to the fullest extent and also to enable the free ow of line pressure through the desired ducts at the proper time. While we have located our fast-acting cut-off valve in the end portions of the piston in our preferred embodiment, such fast-acting cut-oli valves may be located at any point within the iluid pressure system intermediate the inlet port and the end chambers of the casing. The location of a fast-acting cut-ott valve at any other point in the iiuid pressure system produces considerably less desirable and even at times inoperative results.

One of the problems presented by any vibrator of our type involves the use of a starting mechanism since it is obvious that once the vibrator lhas been used and the line pressure has been cut off from the vibrator, there is a tendency for the piston to come to rest at dead center. There are many special adaptations of starting mechanisms so as to force the piston to come to rest at a point other than dead center. Any such well known starting devices may be employed with equal success in a vibrator of our construction.

While our preferred embodiment consists of a vibrator as above described employing a fast-acting cut-oit valve of the flapper valve type as illustrated in Fig. 5, an alternative embodiment illustrated in Fig. 6 will also achieve very desirable results. As shown in Fig. 6 this vibrator consists of a casing 30 having an inlet port 31 and exhaust ports 32. Mounted for reciprocatory movement inside the casing 30 is a piston 33. This alternative embodiment as illustrated in Fig. 6 is a vibrator similar in construction to that described above except that the piston 33 is the fast-acting cut-oit valve. This is accomplished by the critical location and size of the interior ducts of the piston 33. Air under pressure is introduced to the system through inlet port 31 which leads to circular chamber 34. When the piston 33 is slightly to the left of that as illustrated in Fig. 6, circular chamber 34 is in Contact with the opening of duct 35. Thus the air under pressure flows through duct 35 into end chamber 37 Where such air under pressure tends to force the piston 33 to the right. As the piston moves to the right contact is established between circular chamber 34 and duct 3S and contact between circular chamber 34 and duct 35 is eliminated. Thus, air under pressure commences flowing through duct 38 into end chamber 39 tending to decelerate the move- However, the momentum of the movement of the piston 33 to the right carries thepiston 33 beyond the point where full contact the right. 'Such increased pressure thus decelerates the movement of the'piston to the right at an increased rate v and further accelerates the movement of the piston to the left to complete the cycle. Small groove 4t) is provided as a fast starting aid should piston 33 come to rest at the `-`right-end Qf. theucasingsand accordingly intorder .to achieve ithe maximum, efficiency, thisgroove 40. should be asnarrow as possible to permitjthe `relatively effective sealing of end chamber 39 and yet pro-videa smallpoint of entry for the air to reach duct 3.8 ,when the piston 33 is at the right end of the casing 30. Satisfactory starting results may, however, be achieved by .controlled leakage of air pressure between the piston, and casing-walls.. As the piston 33 moves tothe leftandpasses fdead .center the ,contactV between-circular chamber V34 and duct 38 is broken and co-ntact between circular chamber 34 and duct 35 is established. The air passing through duct 35 commences the deceleration o-f themovement ofthe .piston to the left. As the piston continues to move to the left air issubstantially sealed inend chamber37 in the same manner that duct 38, operated in relation to end charnber 39.

Instead of a very small ,groovet40, -it hasl been found that construction of these` devices=with ordinarypistoncylinder clearances of themagnitude in accordance with v the following tableY will permit self-starting:

Variation from these ranges within the ordinary skill of the art is to be expected, these ranges indicating suitable clearance ranges between the piston and the cylinder for devices in accordance with this invention.

When the sealing of the end chamber takes place as above described, the distance remaining between the end of the piston and the end of the cylinder we call end clearance. All ports are cutoff leading to and from the end chamber so sealed. Thus, increased deceleration of the movement of the piston to the left and increased acceleration of the movement of the piston to the right are achieved.

From the discussion above relating to the mode of operation of our vibrator as illustrated in Fig. 6, it will be appreciated that the location and -size of ducts 35 and 38 in relation to circular chamber 34 are very critical. Thus, alternative exclusive contact between ducts 35 and 38 with circular chamber 34 during movement of the piston 33 in the relatively central portion of the casing is established and the substantial elimination of such contact is achieved between ducts and 38 with circular chamber 34 during such reciprocating movement of the from each relatively end portion of Vthe casing30. It will also be observed that the combined effective widths of the circular chamber 34 and'either duct 35 or 38 at their point of surface contact must be less than the distance the piston 33 may travel in any onedirection from dead center. Such effective widths do not include small grooves 40 or 41. since such components are each very small and do not disturb the effective -width of ducts 35 and 3S. While our alternative embodiment produces superior results over that heretofore achieved in vibrators not embodying a fast-acting cut-off valve, our vibrator as illustrated in Fig. 6 has-been found to possessup to about 90 percent of the increase in power obtained with our vibrator previously discussed which involved pressure responsive fast-acting cut-off valvesflocated in the fluid` pressure system.v The alternative embodiment of our vibrator is particularly well adapted to vibrators of smaller size where the installation of ai -appertypeifastactng cut-off valve would be difficult and costly. .Referring more particularly to Figs. 7, 8 and 9, there piston y33 approaching and departing `r.is shown .a seriesv of=views`of thesam'evibratorin which the piston.14 `is in variousl positions; In-.'Fig. 7,'for example, the piston 14 is in neutral position. It will be observed that inthis position in the embodiment here shown, all ports leading into and out of the device are closed.

In Fig. 8, the piston 14 has moved to the left so that internal duct 35 and its entry means 43 are in operative communication with the recess 34 and pressurized gas may flow freely through the inlet duct 31, the recess,34, the piston entry means 43 and theinlet duct 35 into the left end chamber 37. Exhaust means32 to the left are closed by the piston 14. .The inertia. 0f the piston 14 carries the piston farther to the left as shown in Fig. 9 whereby all of the entry and exit ports 32 and 34 are closed by the piston body 14. The air in end chamber 37 is now under relatively highcompression, serving to stop the movement of the piston to the left and to accelerate it to the right. The air in the end chamber 39 is now at atmospheric pressure and little resisance is offered to the movement of the piston to the right. As the piston then moves to the right, the exhaust ports 32 are first closed, and simultaneously or immediately thereafter opn erative communication betweeny the inlet duct 38 andthe .50 the reciprocating annular groovef34 is established, and the gas pressure in end chamber 39 is elevated to atl least about line pressure.

J ust prior to the closing of the exhaust ports 32 exiting from end chamber- 39, inlet duct 35 has again come into operative communication with annular groove 34 and another` charge of pressurized gas introduced into end chamber 37. `Due tolleakage of the gas through Vthe clearance, and the change inY temperature of the gas due to the compression in an area surrounded by a good heat conductor and the cooling effect of the expansion of the compressed gas, the pressure in the end chamber 37 at the time registration betweenthe entry means 43 and the annular groove 34 is .re-established is less than line pressure and hence ;a boosting-effect is secured rather than a feed-back of pressure into-the line 31.

Thisoperation is thenrepeated Afor-the right hand end of the device. In the foregoing Figures 7 9, the piston 14 is serving a-s itsown fast-acting.r cut-off valve,vand the clearance between the piston 14 and the cylinder wall 1 serve as the self-,starting means.

YIn orderA to illustrate thesuperiororesults attained by our invention as more particularly described above,` we present below data clearlyfillustrating vthe increased horsepower and greater` frequency produced by-vibrators employing our .inventions These tests were runupon our vibrators incorporating the-'preferred embodiment of our invention asillustrated iniFigs. l-5 as described above and employed a singl'e'vibrator'without the addition of our fast-acting cut-off valveaand further theresults attained by employing/.inthe same 'devicewhen our fastacting cut-otfvalve wasxadded to the vibrator at the points illustrated in Fig. 2' :The liney pressure given below is presented in pounds per square inch while the power is Vmeasured in unitsof horsepower vtimes a constant.

Our vibrator Our vibrator not employemploying Line Pressure, p. s. i. v ingafast-actourfast-aeting ing cutoff cut-oft valve,

valvefHPXC HPXG Further results upon our vibrator indicate a vastly superior frequency at a given line pressure.

Thus, it is clear thatwith a given supply line pressure, the vibrational energy of thisV vibrator is increased many times over that embodied in the present form of vibrator which does not include our fast-acting cut-olf valve. It is equally apparent that the frequency of vibration will also be greatly increased, producing superior results.

In the data presented above, the readings relating to a vibrator not employing a fast-acting cut-off valve terminate at approximately 100 p. s. i. since at that point the impacting of the piston against the ends of the casing made further readings extremely difficult and relatively inaccurate. The vibrator tested when employing our fast-acting cut-off valves provided a further increase in vibrationpower with increasing pressure without the damaging impact of piston against the ends of the casing. Hence an increase in relative energy may be secured by an increase in line pressure rather than the usual steps of resorting to a larger sized vibrator. In the above tests the same vibrator was used for all tests, the only variable being the addition of a fast-acting cut-off valve for comparison.

Referring more particularly now to Fig. l0, there is hereillustrated the meaning ofend clearance at cut-off. The distance d between the left hand end of the piston 14 and the inner face of the plug 44 is the end clearance at cut-off. The dotted line 45 indicates the approximate additional travel of the piston 14 during which time the gas in the end chamber 37 is under compression. As in the earlier devices, the compression of the gas prevents impacting of the piston 14 with the inner face of the plug 44. However, the structure' and operation of the prior devices did not permit the utiliza- Y tion of power to the surprising extent afforded by the devices of the present invention.

Thus, it is clear that with a given supply line pressure, the vibrational energy ofV this vibrator is increased many times over that embodied in the present form of vibrator which does not include our fast-acting cut-off valve. It is equally apparent that the frequency of vibration will also be greatly increased, producing superior results.

In the data presented above, the readings relating to a vibrator not employing a fast-acting cut-off valve terminate at approximately 100 p. s. i, since at that point the piston impacts against the ends of the casing. This limitation on operating pressure of about 100 p. s. i. seems to apply to conventional vibrators not utilizing compression above line pressure. when employing our fast-acting cut-off valve provided a further increase in vibrational power up to 3.5 times with increasing pressure to 150 p. s. i. without the damaging impact of 'piston against the ends of the casing. Hence an increase in relative energy may be secured by an increase in line pressurerath'er than the usual steps of The vibrator tested 8 resorting to a larger sized vibrator. In the above tests the same vibrator housing was used for all tests the only variable being the addition of a fast-acting cut-ott valve for comparison.

Referring more particularly now to Fig. 10 there is here illustrated the meaning of end clearance at cut-off. The distance d" between the left hand end of the piston 14 and the inner face of the plug 44 is the end clearance at cut-olf. The dotted line 45 indicates the approximate ultimate travel of the piston 14 during which time the gas in the end chamber 37 is under compression. In the earlier devices, pressure of a magnitude near line pressure of the gas prevents impacting of the piston 14 with the inner face of the plug 44. Unlike. the earlier art, movement o-f the piston through the end clearance after cut-off and up to the terminal position (45 in Fig. l0) compresses the gas well above line pressure due to the absence of any possible means of feedback to the supply line or escape to the atmosphere. The structure and operation of the prior devices did not permit the utilization of power to the surprising extent aorded by the devices of the present invention.

The length of the internal ducts 35 and 38 longitudinally of the piston is in all cases, as shown in Figs. 2, 3, 6 and 7 through l0, more than 1/9. the length of the piston and less than about of the length thereof. By so constructing and arranging the internal ducts 35 and Y 33, the stroke of the piston is lengthened to a point where there is sufficient acceleration which in combination with the mass of the piston provides suicient inertia to compress the gas in the end chambers to a point not heretofore achieved and thereby vastly improve the power output of the device. If the internal ducts 35 and 38 are longer than about @A of the length of the piston, the stroke becomes so long before introduction of gas at line pressure that the device will either impact or, if the cylinder is long enough, the opposite end of the piston may pass the inlet annular groove 34 and cause the piston to become locked in an extreme position. Thus, the point at which the internal ducts 35 and 38 rise to the surface of the piston is important in determining the stroke of the piston and the end clearance at cut-off. The amount of end clearance at cut-off determines the rate of compression of the gas and thus the power and the frequency as shown in Figs. l1 and 12. These can be varied within reasonable limits depending upon the length of the piston and the power requirements thereof.

' The end clearance represented by d varies vwithin the range of a minimum of about 5% of the length of the piston to a distance which is less than the length of the piston diminished by the sum of the length of'an internal duct such as 35 or 38 plus the width of the annular groove 34. Also, the sum of the width of one entrance port 43 and the width of the annular groove should be less than the axial width of the end chamber fed by that port, the latter width measured at neutral position. This relationship should be followed whether there is only one annular groove 34 or whether there are two such grooves. When the piston and cylinder are constructed in accordance with these limits, locking of the piston in an extreme position cannot occur and best results from the standpoint of power and frequency are secured.

The basic objective in the design and positioning of the iluid system components is to secure a filling of the end chambers with liuid at as near to line pressure as possible during a portion of the stroke and permitting the chambers to be closed during another portion of the stroke lwherein the fluid is compressed to a relatively high pressure in excess of line pressure, and allowing the compressed fluid to substantially expend itself against the piston instead of exhausting it to the outside or feeding it back into the line.

The positioning of the exhaust ports withrespect to f down.

agences the piston is of some importance although not critical. `When the piston is in neutral position as shown in Fig. 7, the exhaust ports should be closed forvbest results. In -other words, the distance between the exhaust ports measured as over-all distance from the outer extremity of each port should beno more than about the length of- :the piston. These ports may be positionedva distance apart :which isA somewhatdess than the vlength of the piston although the displacement toward the center of the cylinder should be small-and never inexcess of the end clearance. Ifl the displacement exceeds the end clearance, then the inlet port 43 of the piston may come into registry -with-an exhaust port 32 causing-a premature release of pressure from the end chambers and a consequent loss of power.

Accordingly, for the greatest utilization of the power available in the compressed gas, the dimensions of the piston and the relationships thereof to the location of the exhaust ports and the internal ducts of the piston as given above and illustrated in the'drawingsrshould be followed.

Fig. 11 shows the results obtained with various end clearances at' 100 lbs. per' square inch gauge in terms of cycles per minute. It is almost a straight line function,

the number of cycles per minutevarying substantially -inversely with the length of theend clearance at this pressure. The device which was used in these tests was a 1% inch diameter piston having a length of 2 inches, the diameter of the entry means 43 and the width o-f the annular groove 34 being .125 inch.l The distance be'. -tween the exhaust ports (overall) was exactly the length ofthe piston. .218 inch.

In Fig. 12, the power has been plotted against end clearance and again there is an inverse substantially A practical valve of end clearance is -straight line function showing a decrease in power as Vthe end clearance is increased.

Of course, there are practical limits and, for a 3A inch piston, an end clearance o-f approximately .16 inch at cut-off is about the minimum. An optimum clearance at cut-off is, for a 1 3%: inch piston, in the range of .2 to .3 inch.

It isequally clear from the above description of this improved vibrator that'it is virtually impossible for the thermore, such action by the piston in striking the lend Aportions of the casing presents a problem as to rapid wear and shock destructive to the mechanism itself. The vibrator of this invention rectifies this problem, as it is virtually impossible for the piston to strike the end portions of the casing. However, as has been earlier noted, the ridge 27 is provided as a precautionary measure to protect the fast-acting cut-off valve should the piston approach too closely to the end portion of the casing,

either'while in operation or when coming to rest or shut The vibrator of this invention also provides a device which may be more minutely controlled in its operation, as well as providing an increased power and frequency for the given energy content of the pressurized gas.

' l `Vibrators in accordance with this invention are useful in any of the well known applications for these devices. For example, these noiseless orsemi-noiseless vibrators Vcan bevused to drive conveyors of dry materials, e. g., grain or sand, to compact aggregate in molds `in the V"manufacture of concretel blocks, to maintain constant feed from hoppers. to be vibrated by bolts. Compressed air at line pressures The device is simply athxed to the unit of from about 10 to about 150 p. s. i. may be used for the aforesaid purposes.

. Other modes of applying,theqprinciple of this invention may be employed insteadof-those specically set forth above, changes being made as regardsV theY details herein disclosed, providedthe :elements set forth in'any of the following-claims, ortzthe equivalent of such be employed.

It is, therefore, particularly pointedout and distinctly claimed as the invention:

1. A vibration device comprising a casing, a piston supported for reciprocatory movement within said casing, said casing having: an inletportpositioned midway of its length for transmitting fluidfunder pressure, and exhaust ports located'near' each end thereof, said piston being longer than the distance between said exhaust ports and having a rst entrance portpositioned in the wall thereof tothe right ofthe mid-point `of said piston in communication with the left end thereof, and a second entrance port positioned in the wall thereof to the left of the mid-point ofv said piston in communication with the right end thereof, said entrance ports being located for alternative registry with theinlet port of said casing during reciprocatory movement of the piston, whereby,

when said piston is' positioned at dead center in said casing, said first entrance port communicating with the left end of said pisto-n is to the right of said inlet port and said second entrance port communicating with the right end of said piston is to the left of said inlet port, and valve means at the ends of said piston operative in response to a pressure differential to seal off each of said inlet po-rts when the piston intimately approaches each end thereof whereby to provide a cushion of pressure fluid. Y

2. A vibration device comprising a closed cylinder, a piston supported for reciprocatory movement within said cylinder, said cylinder having an inlet port positioned midway of its length for transmitting gas under pressure, and exhaust ports locatedv neareach end thereof, said piston being of suflicient length to close all exhaust ports simultaneously, said pisto-n having a single inlet Dort positioned in the wall thereof tothe right of the mi-d-point of said pisto-n in communication with an internal duct exiting at the left end thereof, and another single inlet port positioned in the wall thereof to the left of the mid-point of said piston in communication with a separate internal duct exiting at the right end' thereof, said inlet ports being located for -alternative registry 4with the inlet port of said cylinder during reciprocatory movement of the piston, -whereby when said piston is positioned at dead center in said cylinder, said first inlet port cornmunicating with the left end of said piston is to the right of said inlet port and said second inlet port communicating with the right end of said piston is to the left of saidinlet port of said cylinder, said piston constituting valvel means operative in response to a pressure differential to alternately seal off each of said inlet ports and said exhaust ports when the piston intimately approaches each end thereof, whereby to pro-vide a cushion of gas under pressure. v

3. A vibrator comprising a closed cylinder, a piston reciprocably supported withinV said cylinder, said cylinder having an annular'groove in its mid-section, duct means opening into said groove for the introduction of pressurized gas thereto, exhaust ports located on either side of and substantially equidistant from said annular groove for the release of spent gas, internal ducts formed within said piston opening at opposite ends thereof and each having single. entry means7 through the side of said piston alternatively registerable with said annular groove, the distance longitudinally of the piston between said entry means and the exit of the internal duct fed thereby, being more than V2 the length of the piston and less than about 2%; thereof.

4. A vibrator comprising a closed cylinder, a piston reciprocably supported within said cylinder, said cylinder having an annular groove in its mid-section, duct means opening into said groove for the introduction of pressurized gas thereto, exhaust ports located on either side of and substantially equidistant from said annular groove for the release of spent gas, internal ducts formed within said piston opening at opposite ends thereof and each having single entry means through the side of said piston alternatively registerable with 'said annular groove, the distance longitudinally of the piston between said entry means and the exit of the internal duct fed thereby, being more than 1/2 the length of the piston and less than about 2%: thereof, the end clearance at cut-off being greater than about of the length of the piston and less than L-(l-i-w) Where L is the length of the piston, I is the longitudinal length of an internal duct, and w is the width of the annular groove.

5. A vibrator comprising a closed cylinder, a piston reciprocably supported within said cylinder, said cylinder having an annual groove in its mid-section, duct means opening into said groove for the introduction of pressurized gas thereto, exhaust ports located on either side of and substantially equidistant from said annular groove for the release of spent gas, the overall distance between said exhaust ports measured from the outer extremities thereof being less than the length of said piston, internal ducts formedwithin said piston opening at opposite ends thereof and each having single entry means through the side of said piston alternatively registerable with said annular groove, the distance longitudinally of the piston between said entry means and the exit of the internal duct fed thereby, being more than 1/2 the length of the piston and less than about @A thereof, the end clearance atcut-off being greater than about 5% of the length of the piston and less than L-(l-t-w) Where L is the length of the piston, l is the longitudinal length of an internal duct, and w is the width of the annular groove.

6. A vibrator comprising a closed cylinder, a piston reciprocably supported within said cylinder, said cylinder having an annular groove in its mid-section, duct means opening into said groove for the introduction of pressurized gas thereto, exhaust ports located on either side of and substantially equidistant from said annular groove for the release of spent gas, the overall distance between said exhaust ports measured from the outer extremities thereof being no more than about the length of the piston, internal ducts formed Within said piston opening at opposite ends thereof and each having single entry means through the side of said piston alternatively registerable with said annular groove, the ditance longitudinally of the piston between said entry means and the exit of the internal duct fed thereby, being more than /2 the length of the piston and less than about 3/4 thereof, the end clearance at cut-off being greater than about 5% of the length of the piston and less than L-U-l-w) where L is the length of the piston, l is the longitudinal length of an internal duct, and w is the width of the annular groove.

7. A vibration device comprising a closed cylinder, a piston supported for reciprocatory movement withinsaid cylinder, said cylinder having an inlet port communicating with an annular groove positioned midway of its length for transmitting gas under pressure to said piston,

and'exhaust ports located near each end of said cylinder,v

said piston being of sutlicient length to close all exhaust ports simultaneously, said piston having a single inlet port positioned in the wall thereof to the right of the mid-point of said piston'in communication with an internal duct exiting at the left end thereof and another single inlet port positioned in the wall thereof to the left of the mid-point of said piston in communication with a separate internal duct exiting at the right end thereof, said inlet ports being located for alternative registry with the annular groove of said cylinder during reciprocatory movement of the piston, whereby when said piston is positioned at dead center in said cylinder, the rst inlet port communicating withthe left end of said Vpiston is to the right of said annular groove and said second inlet port communicating with the right end of said piston is to the left of said annular groove of said cylinder, said piston constituting valve means operative in response to a pressure differential to alternatively seal ot each of said inlet ports and said exhaust ports when the piston intimately approaches each end of said cylinder whereby to provide a cushion of gas under pressure.

8. A vibration device in accordance with claim 7 in which said exhaust ports located near each end of the cylinder are substantially the same distance from the annular groove positioned midway of the cylinder.

9. A vibration device in accordance with claim 8 in which the distance between the outer extremities of the exhaust ports is equal to the length of the piston.

10. A vibration device comprising a closed cylinder, a Vpiston supported for reciprocatory movement Within said cylinder, said cylinder having an inlet port positioned midway of its length for transmitting gas under pressure, and exhaust ports located near each end thereof, said piston being of sufficient length to close all exhaust ports simultaneously, said piston having a single inlet port positioned in the wall thereof to the right of the mid-point of said piston in communication with an internal duct exiting at the left end thereof, and another single inlet port positioned in the wall thereof to the left of the mid-point of said piston in communication with a separate internal duct exiting at the right end thereof, said inlet ports being located for alternative registry with the inlet port of said cylinder during reciprocatory movement of the piston, whereby when said piston is positioned at dead center in said cylinder, said rst inlet port communicating with the left end of said piston is to the right of said inlet port and said second inlet port communicating with the right end of said piston is to the left of said inlet port of said cylinder, said piston constituting valve means operative in response to a pressure differential to alternately seal olf each of said inlet ports and said exhaust ports when the piston intimately approaches each end thereof, whereby to provide a cushion of gas under pressure, the end clearance at cut-olf being greater than about 5% of the length of the piston and less than L-(l-l-w) where L is the length of the piston, l is the longitudinal length of an internal duct and w is the Width of the inlet port of said cylinder. t

1l. A vibration device comprising a closed cylinder, a piston supported for reciprocatory movement within said cylinder, said cylinder having an inlet port communicating with an annular groove positioned midway of its length for transmitting gas under pressure to the piston, and exhaust ports located near each end thereof, said piston being of suicient length to close all exhaust ports simultaneously, said piston having a single inlet port positioned in the wall thereof to the right of the mid-point of said piston in communication with an internal duct exiting at the left end thereof and another single inlet port positioned in the wall thereof to theleft of the mid-point of said piston in communication with a separate internal duct exiting at the right end thereof, said inlet ports being located for alternative registry with the annular groove of said cylinder during reciprocatory movement of the piston, whereby when said piston is positioned at dead center in 'said cylinder, said first inlet port communicating with the left end of said piston islto the right of said annular groove and said second inlet port of communicating with the right end of said piston is to the left of said annular groove, said piston constituting valve means operative in response to a pressure differential to alternately seal off each of said inlet ports and said exhaust ports when the piston intimately Vap- 13 14 proaches each end of said cylinder whereby to provide a References Cited in the file of this patent cushion of gas under pressure, the end clearance at cutoff being greater than about 5% of the length of the UNITED STATES PATENTS piston and less than L( l-l-w) where L is the length of the 1,940,388 Callahan Dec. 19 1933 piston, l is the longitudinal length of an internal duct, 5 and w is the Width of the a ular groove. 2,787,251 Becker Apr. 2, 1957 UNITED STATES PATENT oEETcE Certificate of Correction Patent No. 2,861,548 November 25, 1958 Warren C. Burgess, Jr. et al.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent Should read as corrected below.

Column 7, line 46, for 21 read d; Same column 7, line 57, beginning with ThuS, it is clear Strike out all to and including present invention. in column 8, line 22; column 9, line 32, for valve read value; column 11, line 21, for annual read annular; column 12, line 71, before communicating Strlke out of; column 13, line 4, for the mathematical quantity L (Zi-fw) read L- (Zd-fw) Signed and Sealed this 10th day of March 1959.

[SEAL] Attest: KARL H. AXLTNE, ROBERT o. WATSON, Attestzng Officer. Commissioner of Patents. 

